Wireless telecommunication systems are well known in the art. In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS and EDGE are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.
A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1a. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), known as User Equipments (UEs) in 3GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs is connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.
Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station's timing. In 3GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator's networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers. The gateway mobile services also receives and administers connection requests from subscribers from external networks.
The RNCs generally control internal functions of the UTRAN. The RNCs also provide intermediary services for communications having a local component via an Iub interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS.
Typically an RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection. Background specification data for such systems are publicly available and continue to be developed.
In general, commercial wireless systems utilize a well defined system time frame format for the transmission of wireless communication signals. In communication systems such as Third Generation Partnership Project (3GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems, multiple shared and dedicated channels of variable rate data are combined for transmission.
There are four defined states in the Universal terrestrial radio access (UTRA) RRC Connected mode currently specified in 3GPP TS 25.331: Radio Resource Control (RRC) Protocol Specification as illustrated in FIG. 1b. These states include two duplex states, CELL_DCH and CELL_FACH, and two monitoring states CELL_PCH and URA_PCH. These states allow the UTRAN to allocate resources to the User Equipment (UE) on a demand basis.
The CELL_DCH state is a duplex state characterized by:
A dedicated physical channel is allocated to the UE in uplink and downlink.
The UE is known on cell level according to its current active set.
Dedicated transport channels, downlink and uplink (TDD) shared transport channels, and a combination of these transport channels can be used by the UE.
The CELL_DCH state is entered from an Idle Mode through the setup of an RRC connection, or by establishing a dedicated physical channel from the CELL_FACH state. A PDSCH may be assigned to the UE in this state, to be used for a DSCH. In TDD a PUSCH may also be assigned to the UE in this state, to be used for a USCH. If PDSCH or PUSCH are used for TDD, a FACH transport channel may be assigned to the UE for reception of physical shared channel allocation messages.
Transition from CELL_DCH to Idle Mode is realized through the release of the RRC connection. Transition from CELL_DCH to CELL_FACH state occurs when all dedicated channels have been released, which may be via explicit signaling (e.g. physical channel reconfiguration, radio bearer reconfiguration, radio bearer release, radio bearer setup, transport channel reconfiguration, etc.) or at the end of a time period for which the dedicated channel was allocated. Transition from CELL_DCH to CELL_PCH state occurs via explicit signaling (e.g. physical channel reconfiguration, radio bearer reconfiguration, radio bearer release, radio bearer setup, transport channel reconfiguration, etc.). Transition from CELL_DCH to URA_PCH state occurs via explicit signaling (e.g. physical channel reconfiguration, radio bearer reconfiguration, radio bearer release, radio bearer setup, transport channel reconfiguration, etc.).
Radio Resource Allocation tasks for the CELL_DCH state are specified. For the DCH, several physical channel allocation strategies may be applied. The allocations can be either permanent (needing a DCH release message) or based on time or amount-of-data. Resource allocation can be done separately for each packet burst with fast signaling on the DCH. For each radio frame the UE and the network indicate the current data rate (in uplink and downlink respectively) using the transport format combination indicator (TFCI). However, in TDD, DCH and DSCH or USCH may be mapped on different CCTrCHs, their TFCI are totally independent. DCH transmission is not modified by the simultaneous existence of DSCH/USCH. If the configured set of combinations (i.e. transport format set for one transport channel) are found to be insufficient to retain the QoS requirements for a transport channel, the network initiates a reconfiguration of the transport format set (TFS) for that transport channel. This reconfiguration can be done during or in between data transmission. Further, the network can reconfigure the physical channel allowing an increase or decrease of the peak data rate. For the uplink data transmission, the UE reports the observed traffic volume to the network in order for the network to re-evaluate the current allocation of resources. This report contains e.g. the amount of data to be transmitted or the buffer status in the UE.
RRC Connection mobility tasks for the CELL_DCH state are specified. Depending on the amount and frequency of data macrodiversity (soft handover) may or may not be applied. The RRC Connection mobility is handled by measurement reporting, soft handover and Timing re-initialized or Timing maintained hard handover procedures.
UE Measurements for the CELL_DCH state are specified. The UE performs measurements and transmit measurement reports according to the measurement control information. The UE uses the connected mode measurement control information received in other states until new measurement control information has been assigned to the UE.
Acquisition of system information in the CELL_DCH state is specified. FDD UEs with certain capabilities read system information broadcast on FACH. TDD UEs read the BCH to acquire valid system information. For each acquisition, the UE may need different combinations of system information broadcast on BCH. The scheduling on the broadcast channel is done in such way that the UE knows when the requested information can be found.
The CELL_FACH state is a duplex state characterized by:
No dedicated physical channel is allocated to the UE.
The UE continuously monitors a FACH in the downlink.
The UE is assigned a default common or shared transport channel in the uplink (e.g. RACH) that it can use anytime according to the access procedure for that transport channel.
The position of the UE is known by UTRAN on cell level according to the cell where the UE last made a cell update.
In TDD mode, one or several USCH or DSCH transport channels may have been established.
Transition from CELL_FACH to CELL_DCH state occurs, when a dedicated physical channel is established via explicit signaling (e.g. physical channel reconfiguration, radio bearer reconfiguration, radio bearer release, radio bearer setup, transport channel reconfiguration, etc.). Transition from CELL_FACH to CELL_PCH state occurs when UTRAN orders the UE to move to CELL_PCH state, which is done via explicit signaling (e.g. cell update confirm, radio bearer reconfiguration, etc.). Transition from CELL_FACH to Idle Mode occurs upon release of the RRC connection. Transition from CELL_FACH to URA_PCH State occurs when UTRAN orders the UE to move to URA_PCH state, which is done via explicit signaling (e.g. URA update confirm, radio bearer reconfiguration, etc.).
Radio Resource Allocation Tasks for the CELL_FACH state are specified. In the CELL_FACH state the UE monitors a FACH. It is enabled to transmit uplink control signals and it may be able to transmit small data packets on the RACH. The network can assign the UE transport channel parameters (e.g. transport format sets) in advance, to be used when a DCH is used. Upon assignment of the physical channel for DCH, the UE moves to CELL_DCH state and uses the preassigned TFS for the DCH. If no UE dedicated physical channel or transport channel configuration has been assigned, the UE uses the common physical channel and transport channel configuration according to the system information. For the uplink data transmission, the UE reports the observed traffic volume to the network in order for the network to re-evaluate the current allocation of resources. This report contains e.g. the amount of data to be transmitted or the buffer status in the UE. When there is either user or control data to transmit, a selection procedure determines whether the data should be transmitted on a common transport channel, or if a transition to CELL_DCH should be executed. The selection is dynamic and depends on e.g. traffic parameters (amount of data, packet burst frequency).
In FDD mode, the UTRAN can assign CPCH resources to the UE in CELL_FACH state. When CPCH resources are assigned, the UE will continue to monitor FACHs. When CPCH resources are assigned, the UE will use CPCH for all uplink traffic in accordance with RB mapping. In FDD mode, UTRAN may configure the UE to provide CPCH measurement reports of traffic volume on each CPCH channel used. With these measures, the UTRAN can reallocate network resources on a periodic basis. The UTRAN allocates CPCH Sets to each cell and assigns UEs to one of the cell's CPCH Sets. The UEs can dynamically access the CPCH resources without further UTRAN control.
In the TDD mode, the UTRAN can assign USCH/DSCH resources to the UE in CELL_FACH state. When USCH/DSCH resources are assigned, the UE will continue to monitor FACHs, depending on the UE capability. The UE may use the USCH/DSCH to transmit signaling messages or user data in the uplink and/or the downlink using USCH and/or DSCH when resources are allocated to cell and UE is assigned use of those USCH/DSCH. For the uplink data transmission on USCH the UE reports to the network the traffic volume (current size of RLC data buffers), The UTRAN can use these measurement reports to re-evaluate the current allocation of the USCH/DSCH resources.
RRC Connection mobility tasks for the CELL_FACH state are specified. In this state the location of the UE is known on cell level. A cell update procedure is used to report to the UTRAN, when the UE selects a new cell to observe the common downlink channels of a new cell. Downlink data transmission on the FACH can be started without prior paging. The UE monitors the broadcast channel and system information on BCCH of its own and neighbor cells and from this the need for the updating of cell location is identified. The UE performs cell reselection and upon selecting a new UTRA cell, it initiates a cell update procedure. Upon selecting a new cell belonging to another radio access system other than UTRA, the UE enters idle mode and makes an access to that system according to its specifications.
UE Measurements for the CELL_FACH state are specified. The UE performs measurements and transmits measurement reports according to the measurement control information. By default, the UE uses the measurement control information broadcast within the system information. However, for measurements for which the network also provides measurement control information within a MEASUREMENT CONTROL message, the latter information takes precedence.
Transfer and update of system information for the CELL_FACH state is specified. The UE reads the BCH to acquire valid system information. For each acquisition, the UE may need different combinations of system information broadcast on BCH. The scheduling on the broadcast channel is done in such way that the UE knows when the requested information can be found. When the system information is modified, the scheduling information is updated to reflect the changes in system information transmitted on BCH. The new scheduling information is broadcast on FACH in order to inform UEs about the changes. If the changes are applicable for the UE, the modified system information is read on BCH.
The CELL_PCH state is a monitoring (i.e. non-duplex) state characterized by:
No dedicated physical channel is allocated to the UE.
The UE selects a PCH with a specified algorithm and uses DRX for monitoring the selected PCH via an associated PICH.
No uplink activity is possible.
The position of the UE is known by UTRAN on cell level according to the cell where the UE last made a cell update in CELL_FACH state.
The DCCH logical channel cannot be used in this state. If the network wants to initiate any activity, it needs to make a paging request on the PCCH logical channel in the known cell to initiate any downlink activity.
Transition from CELL_PCH to CELL_FACH state occurs
a) by paging from UTRAN (PAGING TYPE1 message) or
b) through any uplink access.
The release of an RRC connection is not possible in the CELL_PCH state. The UE will first move to CELL_FACH state to perform a release signaling.
Radio Resource Allocation Tasks for the CELL_PCH state are specified. In CELL_PCH state no resources have been granted for data transmission. For this purpose, a transition to another state has to be executed. The UE may use Discontinuous Reception (DRX) in order to reduce power consumption. When DRX is used the UE needs only to receive at one paging occasion per DRX cycle. The UE may be instructed to use a specific DRX cycle length by the network. The UE determines its paging occasions in the same way as for Idle Mode, although in this connected mode state, UTRAN DRX cycle length coefficient is also taken into consideration.
RRC Connection mobility tasks for the CELL_PCH state are specified. In the CELL_PCH state, the UE mobility is performed through cell reselection procedures. The UE performs cell reselection and upon selecting a new UTRA cell, it moves to CELL_FACH state and initiates a cell update procedure in the new cell. After the cell update procedure has been performed, the network may direct the UE to change its state back to CELL_PCH state if neither the UE nor the network has any more data to transmit[0]. Upon selecting a new cell belonging to another radio access system other than UTRA, the UE enters idle mode and makes an access to that system according to its specifications. In case of low UE activity, UTRAN may want to reduce the cell-updating overhead by ordering the UE to move to the URA_PCH State. This transition is made via the CELL_FACH state. UTRAN may apply an inactivity timer, and optionally, a counter, which counts the number of cell updates e.g. UTRAN orders the UE to move to URA_PCH when the number of cell updates has exceeded certain limits (network parameter).
UE Measurements for the CELL_PCH state are specified. The UE performs measurements and transmits measurement reports according to the measurement control information. The UE uses the measurement control information according to the system information when no UE dedicated measurement control information has been assigned.
Transfer and update of system information for the CELL_PCH state is specified. The UE reads the BCH to acquire valid system information. For each acquisition, the UE may need different combinations of system information broadcast on BCH. The scheduling on the broadcast channel is done in such way that the UE knows when the requested information can be found.
The URA_PCH state is a monitoring state characterized by:
No dedicated channel is allocated to the UE.
The UE selects a PCH with a specified algorithm and uses DRX for monitoring the selected PCH via an associated PICH.
No uplink activity is possible.
The location of the UE is known on UTRAN Registration area level according to the URA assigned to the UE during the last URA update in CELL_FACH state.
The DCCH logical channel cannot be used in this state.
If the network wants to initiate any activity, it needs to make a paging request on the PCCH logical channel within the URA where the location of the UE is known. If the UE needs to transmit anything to the network, it goes to the CELL_FACH state. The transition to URA_PCH State can be controlled with an inactivity timer, and optionally, with a counter that counts the number of cell updates. When the number of cell updates has exceeded certain limits (a network parameter), then the UE changes to the URA_PCH State. URA updating is initiated by the UE, which, upon the detection of the Registration area, sends the network the Registration area update information on the RACH of the new cell.
Transition from URA_PCH State to CELL_FACH State occurs:
a) when uplink access is performed by RACH.
b) by paging from UTRAN (PAGING TYPE1 message).
The release of an RRC connection is not possible in the URA_PCH State. The UE will first move to CELL_FACH State to perform the release signaling.
Radio Resource Allocation Tasks for the URA_PCH state are specified. In URA_PCH State no resources have been granted for data transmission. For this purpose, a transition to CELL_FACH State has to be executed. The UE may use Discontinuous Reception (DRX) in order to reduce power consumption. When DRX is used the UE needs only to receive at one paging occasion per DRX cycle. The UE may be instructed to use a specific DRX cycle length by the network. The UE determines its paging occasions in the same way as for Idle Mode, although in this connected mode state, UTRAN DRX cycle length coefficient is also taken into consideration.
RRC Connection mobility tasks for the URA_PCH state are specified. In URA_PCH State the location of a UE is known on UTRAN Registration area level. In this state, the UE mobility is performed through URA reselection procedures. The UE performs cell reselection and upon selecting a new UTRA cell belonging to a URA that does not match the URA used by the UE, the UE moves to CELL_FACH state and initiates a URA update towards the network. After the URA update procedure has been performed, the network may direct the UE to change its state back to URA_PCH state if neither the UE nor the network has any more data to transmit. Upon selecting a new cell belonging to another radio access system other than UTRA, the UE enters idle mode and makes an access to that system according to its specifications.
UE Measurements for the URA_PCH state are specified. The UE performs measurements and transmits measurement reports according to the measurement control information. The UE uses the measurement control information according to the system information when no UE dedicated measurement control information has been assigned.
Transfer and update of system information for the URA_PCH state is specified. The same mechanisms to transfer and update system information as for state CELL_PCH are applicable for UEs in URA_PCH state. The UE is put into the CELL_PCH or URA_PCH state by the UTRAN depending on the traffic activity originating from the UE.
At the access stratum level, the UE is identified either by
a) U-RNTI
b) C-RNTI
While using the common transport channels (e.g., RACH, FACH, PCH), UTRAN recognizes the UE using one of the above identifiers. C-RNTI gets deleted when entering the CELL_PCH or URA_PCH state. It also gets deleted when UE reselects a cell for communication via a different base station, even while in a CELL_FACH state.
Whenever the UE transitions from CELL_PCH or URA_PCH state to CELL_FACH state, it performs a respective Cell Update or URA Update procedure. Also, if the UE does not have a valid C-RNTI in the CELL_FACH state, such as when reselecting a cell, it needs to get one from the UTRAN via the Cell Update procedure. The UE transmits a CELL_UPDATE or URA_UPDATE message on the common control channel (CCCH). A CELL_UPDATE_CONFIRM response message is built and sent by the UTRAN on either on a CCCH or DCCH.
FIGS. 2a and 2b illustrate successful Cell Update scenarios. FIG. 2a shows the basic flow without a response from the UE; FIG. 2b shows the basic flow with a response from the UE in accordance with 3GPP TS 25.331: Radio Resource Control (RRC) Protocol Specification. The URA Update procedure is similar.
As noted above, all of the existing connected mode UE state transitions, except coming out of CELL_PCH or URA_PCH, are UTRAN directed (i.e. UTRAN orders UE to be come into the indicated state). In comparison, the UE is configured to transition out of the CELL_PCH or URA_PCH monitoring states depending on events occurring at the UE. As stated above, these transitions take place in connection with either a Cell Update or URA Update procedure which procedures are initiated by the UE entering the CELL_FACH duplex state.
The applicable standard specifications (including 3GPP TS 25.331: Radio Resource Control (RRC) Protocol Specification, and 3GPP 25.321: Medium Access Control (MAC) Protocol Specification) state that the UE enters CELL_FACH state when a Cell Update or URA Update procedure starts. This is intended because a CELL_UPDATE_CONFIRM or URA_UPDATE_CONFIRM message can be received on a DCCH, which is unavailable in the CELL_PCH or URA_PCH state. However, the inventors have recognized a problem with this transition, since the UE is without a temporary identifier, such as a C-RNTI, until a response to the update procedure is received by the UE. Also, the inventors have recognized a problem due to the UE losing its C-RNTI when it reselects a cell in the CELL_FACH state.
For mapping the DCCH or DTCH logical channels over RACH (transport channel for uplink), UE MAC uses the C-RNTI in MAC data PDU header (see standard 3GPP 25.321: Medium Access Control (MAC) Protocol Specification). As a result, the DCCH or DTCH transmission over RACH is not feasible unless the UE has a C-RNTI. On the other hand, the UTRAN can send downlink DCCH or DTCH messages over FACH, by using the U-RNTI in the MAC data PDU header. Hence the inventors have recognized that the UE can only have a half duplex downlink link for DCCH or DTCH until it has a C-RNTI.
Two manifestations of the problem identified by the inventors with the state configurations currently specified in 3GPP TS 25.331: Radio Resource Control (RRC) Protocol Specification are set forth below in connection with FIGS. 3 and 4.
FIG. 3 illustrates problematic UE behavior where the UE is placed in the CELL_FACH state without a C-RNTI to initiate a Cell Update procedure. As shown in FIG. 3, the UE starts in a monitoring state, in this case the CELL_PCH state. An event occurs requiring the Cell Update procedure. Under current specifications, the UE is transitioned into the duplex CELL_FACH state in order to perform the Cell Update procedure which requires an uplink initiation by the UE. In the CELL_FACH state, the UE then sends the appropriate request via a CELL_UPDATE message which is received by the UTRAN. The UTRAN processes the CELL_UPDATE message and responds with a CELL_UPDATE_CONFIRM message that includes a temporary identifier such as a C-RNTI.
This is problematic where another event occurs that requires uplink messaging before the UE receives the CELL_UPDATE_CONFIRM message, i.e. before it receives the C-RNTI. Upon entering the duplex CELL_FACH state, the UE supports all the RRC procedures applicable to CELL_FACH state. For example, it is then specified as being configured to perform ‘Initial Direct Transfer’ or ‘Uplink Direct Transfer’ such as set forth in 3GPP TS 25.331 that require DCCH or DTCH uplink transmissions. However, when the UE is in the CELL_FACH state but without a C-RNTI, the UE has only a half duplex (downlink) DCCH. As a result, the UE is not able to transmit ‘Initial Direct Transfer’ or ‘Uplink Direct Transfer’ messaging resulting in a failure to properly transmit such uplink messaging which it should be capable of when in the CELL_FACH state. A number of such scenarios are possible because the UE non-access stratum has two independent state machines for circuit-switched (CS) and packet-switched (PS) services. Both of these utilize the common RRC connection or in other words the common RRC state.
A variation of the problem that has been recognized by the inventors occurs where Periodic Cell or URA Updates are processed. A high priority Cell or URA Update can be delayed due to UE's operation in the CELL_FACH state while it is without a C-RNTI. For example, as illustrated in FIG. 4, the UE in the CELL_PCH state initiates a periodical cell update procedure by transitioning to the CELL_FACH state and transmitting a CELL_UPDATE message that indicates that it is a periodic cell update request. The UTRAN upon receiving such a period request treats it as a request for information, not resources, so that the UTRAN responds with a CELL_UPDATE_CONFIRM message with the requested information and a command for the UE to return to the CELL_PCH state. However, if in the interim the UE detects uplink data to transmit, the UE may not be able to send a cell update request with this high priority cause (uplink data transmission), until it has possibly returned to the CELL_PCH state again. This scenario is illustrated in FIG. 4, showing the high priority cell update getting delayed.
In view of the problem recognized by the inventors, it is desirable, to provide a WTRU such as a UE that has a connection mode configuration that includes a transition state to implement transitioning to a duplex state where a temporary identifier is supplied to facilitate duplex communications in the duplex state.